Busy box Read file line by line

Question

There is no read applet comming with busy box.

Is there any way to read a txt file line by line using busybox?

What I have now is

while read line
do
     echo $line
done < "$InputFile"

Solution

read is a shell builtin (it couldn't set a shell variable if it were not).

So, if your busybox sh is based on ash, it's:

while IFS= read -r line <&3; do
  printf '%s\n' "$line"
done 3< "$InputFile"

Like in any POSIX shell. But like with any shell, using while read loops to process text is generally bad shell scripting practice.

Above, you need:

• IFS= otherwise leading and trailing unescaped spaces and tabs are stripped from the lines
• -r, otherwise backslashes are treated as an escape character and removed (unless escaped)
• printf, not echo which wouldn't work for lines that are for instance -nene
• "$line" quoted (not $line) otherwise the content of the line is split on spaces and tabs, and globbing patterns expanded.
• <&3 and 3< ..., if you need access to the original stdin within the loop.

If the file contains characters after the last line and you want to display them, you can add after the loop:

[ -z "$line" ] || printf %s "$line"

Note that that loop cannot handle binary data (the NUL character).

Comments

[jordanm]

That doesn't work? Busybox uses ash for a shell, which is not POSIX complaint, but still includes a POSIX read.

[Gilles 'SO- stop being evil']

See also Understanding IFS, Why is while IFS= read used so often, instead of IFS=; while read..?, In while IFS= read.., why does IFS have no effect?, …

[jordanm]

This looks like unnecessary complexity to what should be a working example from the OP.

[Stéphane Chazelas]

@jordanm, I've edited the answer to give reasons for the added complexity.

[Stéphane Chazelas]

Why do you need to prefix busybox to every command? Are you not entering that command line in busybox shell? Does that shell not have a read builtin? (what does type read tell you there?).

[limovala]

@StephaneChazelas I am writing this script for an embedded device, so to make sure the busybox applet is called instead of the actual command, I use busybox prefix I am using Bourne shell '/bin/sh'

[Stéphane Chazelas]

But by doing so you end up using it differently from what your embedded device would (you don't want to call utilities like that as that means reexecuting busybox for every command which is a waste since nowadays busybox can call utilities without reexecuting itself). busybox will call its own commands in priority. If you don't want to call utilities from /bin or /usr/bin, remove those directories from $PATH.

[limovala]

@StephaneChazelas thanks, I will Update my scripts

[Admin]

Maybe it could be better with while IFS= read -r line <&3 || [ -n "$line" ] ; do to avoid repeating the internals of the loop on non-null last line. Yes, it still will not handle a NUL character.